Grounding & Earthing connections

Zero D

Member
2009-08-06 11:11 am
As astx asked for a new thread to discuss the following, i've started this one, following on from Post # 311

http://www.diyaudio.com/forums/soli...ance-class-ab-power-amp-200w8r-400w4r-21.html

Originally Posted by kgrlee in Post # 311

I take it you really mean 'Ground lift devices should be fitted to ALL items.'

Yes & no ! If ALL equipment is Ground/Earth wired as described in my following "Thesis" ;) there would be no need for GL's.

Actually this is of great concern in Medical applications.

And i submit it "could" be in audio too. I'm not aware of ANY investigations/tests etc that have been conducted into this area ?

I think there is at least one EN (IEC standard) laying down the 'law' on this.

Could you provide a link ?

Zero, please post a pic of how you would earth your own amp.

As requested, see my screenie

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True ground Only exists @ the Source ! This is where the signal/s originate.

My observations based on Actual sound system installations, & with regard to grounding each & every piece of equipments metal case Directly to earth via the Mains plug. Plus ONLY grounding @ the source, or the first available point nearest to it/them, ie the PreAmp/Mixer. And engaging All ground lift/s provided, except the source.

If the shield is connected to the chassis at both ends, it WILL create an earth loop = Not good !

Some equipment with a metal case has NO mains Earth connection, & is supplied with a 2 wire mains lead. If possible, it's beneficial to change it to 3 wire lead & earth the case, & then ALSO remove Any/All internal ground connection/s to the case.

In metal rack mounted Pro equipment, unless isolating grommets are used under the screws, an earth loop WILL be created = Not good ! Most "Pro" installs i've seen over the years, are incorrectly grounded, in more ways than one !

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I found an article on here which people might like to peruse etc. It incorporates some of my thoughts & findings.

 

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Some equipment with a metal case has NO mains Earth connection, & is supplied with a 2 wire mains lead. If possible, it's beneficial to change it to 3 wire lead & earth the case, & then ALSO remove Any/All internal ground connection/s to the case.

Hmm yeah that could be problematic. You get someone who files off the polarized plug, large prong being neutral, with metal cases someone might get hurt or worse. ZZZpppptttt! Earth gnd is called saftey gnd for a reason.:)
 
Actually current flowing in the screen is really not a problem, at least in pro gear with sanely implemented interfaces.
SCIN can be trivially fixed with a parallel earth conductor, and adding aditional earth paths is very much less likely to result in a safety problem then removing them is.

In fact the lowest noise levels are usually achieved with as many parallel ground paths as you can manage (Mesh grounding) because it minimises loop area and reducing loop area reduces magnetic coupling.

See Tony Walderons papers amongst others.
Bonding Cable Shields at Both Ends to Reduce Noise
Designing for Interference-free Audio System Components
A Practical Interference Free Audio System (Part 2)

I would never advocate removing a safety ground connection, there is always a safe way to achieve the same result.

Regards, Dan.
 

Zero D

Member
2009-08-06 11:11 am
This thread is MAINLY concerned with achieving the Lowest Hum & Noise. Sure safety is important too.

Originally Posted by AndrewT

ClassII equipment is tested and guaranteed as a completed Black Box. This is termed Double Insulated

I'm aware of that, & it "can" work well.

And you are not allowed to add a PE (Earth wire) to a double insulated, ClassII item.

Quite frankly, i don't give a flying **** what "they" say, i do what works best. And no item i've ever modified has failed a PAT test ! If items are modified as i suggested, it converts them to a safely earthed unit, with All the benefits of correct grounding = :) Maybe "they" need to rethink their info :D
 
However, class II can be converted into a class I appliance provided the work is done in a suitable way and a PE of suitable size provided, and that can then be a safe unit.

The time this becomes difficult is when you have live chassis or similar (Telly!), where obviously great care must be taken, but I would argue that a modification that converts a class II appliance into a class I unit with all the apropriate changes is legitimate.

Obviously modifying a class II appliance and continuing to consider it a class II appliance is a problem.

The takeaway for me is that one does not build class II as DIY, and one does not get clever with the PE connection under any circumstances, every bit of DIY is either SELV or class I and every bit of class I gear has a direct connection to the safety earth in the mains cable.

73 Dan.
 
I really dont get why DIYers still have so many issues with earthing their equipment - there are plenty of articles about it, the best ones I have read are Rods:

Power Supply Wiring Guidelines
Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

Personally here in the UK, i have found that isolating signal ground from the chassis, and connecting the 0V star ground to mains earth gives me safety, and no hum/ground loop issues - as shown in Rod's article above.

Things like "Neutral/Cold used as Ground" are just lousy wiring practices in some countries. The correct fix is to address this at the mains supply, not in the devices.
 

Zero D

Member
2009-08-06 11:11 am
This thread is MAINLY concerned with achieving the Lowest Hum & Noise. Please post accordingly, Thanks ;)

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Originally Posted by dmills

I would never advocate removing a safety ground connection

Neither would i, & i havn't.

Thanks for the links, & your class II convertion info :)

Originally Posted by jaycee

Personally here in the UK, i have found that isolating signal ground from the chassis, and connecting the 0V star ground to mains earth gives me safety, and no hum/ground loop issues

Yes, for all but the source, & with multiple pieces of equipment, the conditions exist for many Grounding/Earthing mistakes to be made, & often are.

The correct fix is to address this at the mains supply, not in the devices.

Care must be taken with EACH unit, both in Grounding & Earthing.
 
This appears to be a response to my recommended earthing scheme for Toni's excellent amp in #297 of 2stageef-high-performance-class-ab-power-amp-200w8r-400w4r I enclose the pic for convenience.

I would be pleased to hear of possible problems if the amp is earthed via (3) in the pic. ie [?] is a direct short to Chassis. This is how I have earthed Power Amps or other physically big items with many In/Outs like a mixer.

It was really about RFI design. The main point is that ALL leads that pierce the Chassis MUST either be connected to it directly or via 100n Ceramic caps with the SHORTEST POSSIBLE LEADS right AT the connector/terminal.

It is what I remember of an Engineering Memo I wrote about designing stuff to meet 'both' Class I & Class II safety standards Internationally and the implications re Hum Loops etc. Even today, there are some markets which don't have a 3rd earthing pin on mains and for these, Class II 'Double Insulated' is appropriate.

With care, electronic stuff can be designed to be easily converted for each of these markets To do so as other than the original manufacturer is illegal in many countries.

From a Hum Loop perspective, Class II 'Double Insulation' is the easiest. This seems to be Zero's favoured solution. But I would be very wary of any big Class II electrical device eg Power Amps. :eek:

For these, Class I 'Earthed Chassis' is appropriate. If you don't do this, you sometimes get little shocks from the chassis and this was common with evil Yankee gear of the 70's & 80's used in da old country.

If you don't mind this, Zero's method will 'work' but you'd better have those 100n ceramics at ALL input sockets. :)

I'll take a stand on having 'one and only one' point of the circuit in ANY box connected to Chassis. At Calrec, this was religiously done. Part of Final Test on a big mixing desk was to remove this Chassis connection (a big Cu strap like a car battery lead) and check that no other connection to Chassis existed.

I invite you to dream up evil cases where the scheme I show in the pic will give problems with a Power Amp. (3) the Star Point direct to Chassis.
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There are actually 2 cases. One is Pro audio where connections are balanced. This is well studied. Self, Jensen, Whitlock, Rod Elliot, Muncy and the zillion papers in JAES etc are appropriate. Sadly there are still 'pro' makers who don't understand this properly which is why we still have the 'pin 1 problem'.

For this 'pro' case, Direct connection to Chassis of the Shield at the SEND end and connection of the shield to to Chassis via 100n Ceramics with SHORT LEADS at the receive end is agreed by the above authorities and works well in 'real life' too.

I don't mean the shield is not connected to the circuit at the receiver. It MUST do this for loadsa reasons including P48V power. I mean you can connect the shield to Chassis via the cap bla bla if you don't connect it directly to Chassis. But you MUST make one or the other connection to Chassis at both ends of the cable.
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For evil, domestic RCA connections, things are less clear. Self, Rod Elliot etc pontificate slightly on this but the permutations are far greater.

If you have Balanced Inputs, you can avoid may problems with evil unbalanced RCA sources.

Only certain Balanced Outputs give good results with evil RCA inputs. Some give VERY poor results indeed.

For stuff like a domestic Power Amp with RCA inputs, again I invite you to dream up evil situations where my scheme will give problems.
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I think there is at least one EN (IEC standard) laying down the 'law' on this.
Could you provide a link ?
I have been a real beach bum from before the turn of the millenium and haven't quite returned to Civilisation. Probably easier for you to find ENs.

The issue is leakage currents including those from caps connected to transformers in bits that are stuck into people.
 

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matze

Member
2012-09-12 5:45 pm
For evil, domestic RCA connections, things are less clear. Self, Rod Elliot etc pontificate slightly on this but the permutations are far greater.

Hi kgrlee,

in my last amp project, I get different results when connecting the RCA input or the star ground point to earth (in both cases via R||C).

The amp is rather low-power with class II isolated transformer. The source (DAC) is connected via RCA, it is class II isolated as well. There is no hum or any other audible noise with either of the earthing variants, but the sound is slightly brighter and less colorful when connecting the star ground to earth. This is "better" for some kind of music, but worse for the other. (Not earthing at all leads to "very colorful" sound, but somewhat restriced sound stage)

I assume that the power supplies of both devices inject noise current into the small-signal path. Therefore, earthing somewhere between the sources, e.g. at the RCA input socket, might be a meaningful decision. If, on the other hand, the amp power supply generates much more current, I would opt for earthing the star ground.

Do you have any suggestion, how one could decide on an objective basis which version is best? Unfortunately, I do not have access to high-frequency measurement equipment. Measuring with the ear is of course fun, but backing the result up would be fun, too.

Best regards,
Matthias
 
Leach discusses this and suggests the input socket Earthing as an alternative that may be better. He also suggests, no insists, that there must be a low inductance connection between Signal ground and Power Ground in the amplifier circuit and suggests a 10r for this.
That same 10r appears in Kgr's version.
 
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matze

Member
2012-09-12 5:45 pm
Leach discusses this and suggests the input socket Earthing as an alternative that may be better. He also suggests, no insists, that there must be a low inductance connection between Signal ground and Power Ground in the amplifier circuit and suggests a 10r for this.
That same 10r appears in Kgr's version.
Hi Andrew,

earthing RCA input socket (via C or R||C) might be the best compromise also in my experience.

Still, I'm wondering whether there are some (tricky?) measurement techniques one can apply in order to not only depend on listening tests when high-frequency equipment is not available.

Cheers,
Matthias
 
Still, I'm wondering whether there are some (tricky?) measurement techniques one can apply in order to not only depend on listening tests when high-frequency equipment is not available.
The Calrec/Tesla CB radio was an AC motor driving a car ignition system. A 1m rod aerial was fixed to the spark plug (All these are Tesla inventions). It was an ALL-BAND transmitter.

I could only run it at night cos every meter in the place (including I'm told the passive VOMs) would go 'blip blip blip'. Shame about TV reception in Hebden Bridge.

If you gear doesn't click with this in the same building, it will be immune to anything short of a lightning strike.

Today, a mobile phone is probably a good practical test. See what happens when it receives a text message.

Cordell has some good recommendations in his book.
 

Bonsai

Member
Paid Member
2003-07-25 10:44 pm
Europe
www.hifisonix.com
I use the low value resistor like Leach does and am getting outstanding results for RFI noise and hum/harmonics.

My pre (X-Altra Mini) and power amp (nx-Amp) chassis are solidly earthed via the 3 wire mains cable. On the pre, the star ground connects directly to the chassis at one point only. In the power amp, the PSU star connection goes to a ground lifter (20A bridge rectifier with 22 Ohm 5W in parallel) - so the star ground in the power amp is floating +-1.4V wrt the chassis with is earthed. The power amp electronics only make the connection to the chassis through the ground lifter and nothing else.

The idea of the 10 Ohm resistor (I am using 15 Ohms) between the front end power amp circuitry and the rest of the circuit is to ensure that the earthing path is forced through the mains earth, and does not take the ground sheath in the audio cable. Works very well indeed.

re the caps at the cable entry point to chassis mentioned by kgrlee above: my Marantz PM6800 uses these extensively on inputs and outputs. I have had this amp for about 12 years and never experienced any RFI problems, so the technique works very well. I can also report that if my pre and power amp are NOT earthed, then they pick up RF. The test for this is to put you mobile next to your power amp or pre-amp and get someone to phone you. If you hear characteristic mobile phone chirping over your speakers - you have a problem. When I connect the earths, there is no pick-up. Let me add, you should not operate any equipment without their safery earths -I am merely pointing this out because earthing your equipment properly has a third benefit (the first two being a) the continuance of your life and b) the reduction of hum) which is reduction/elimination of RFI

My CD/SACD player is a Pioneer 2 wire mains supply. If I connect it via the audio line out to the pre, I get a little bit of noise - it uses an SMPS and the chassis is connected to earth via the audio cable. If I use the optical out and go through my DAC - dead quiet - wonderful.

I will probably do some work on my CD player - throw out that terrible SMPS and fit a solid linear supply with decent 3 pin earth. Alternatively, I could simply bond the SACD chassis to the preamp chassis.

SMPS should be banned from anything playing audio (with apologies to the class D fans and Bruno) - they belong in computers.
 
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SMPS should be banned from anything playing audio (with apologies to the class D fans and Bruno) - they belong in computers.

SMPSUs work better than linear in my experience but only when the filtering's adequately taken care of. The future is very definitely SMPSU-shaped so I suggest getting used to it :D

Listening now to a chipamp fed from a Meanwell 100W 18V unit, sonic nirvana...
 

Zero D

Member
2009-08-06 11:11 am
@ kgrlee

I wonder how much gear these days will pass those Tesla tests. Interesting

I'll take a stand on having 'one and only one' point of the circuit in ANY box connected to Chassis. At Calrec, this was religiously done.

:)

Your RFI screenie might be good for RFI immunity, but i'm wondering if it's also best for hum/GL immunity ?

Originally Posted by Bonsai

My pre (X-Altra Mini) and power amp (nx-Amp) chassis are solidly earthed via the 3 wire mains cable. On the pre, the star ground connects directly to the chassis at one point only. In the power amp, the PSU star connection goes to a ground lifter (20A bridge rectifier with 22 Ohm 5W in parallel) - so the star ground in the power amp is floating +-1.4V wrt the chassis with is earthed. The power amp electronics only make the connection to the chassis through the ground lifter and nothing else.

Good to hear ;)

SMPS should be banned from anything playing audio (with apologies to the class D fans and Bruno) - they belong in computers.

Indeed ! As far as in the small signal domain anyway.